tDIC

So I've been scouring the internet for the last two days and all I can seem to find in pump tuning info.

Truck:
1992 W250 12 valve Cummins
Less than 300 000km (but not sure speedo was broken when I bought it and not sure for how long)
Don't know alot about it's history

Problem:
Last week I drove about 500km round trip (all highway), about half way back (350km ish) I pulled over to clean my headlights, and noticed that it was idling at about 1050rpm.
The idle never went back down
checked lever to make sure that it wasn't being held off the stop by anything while idling. (Cruise and throttle free, and not the problem)
Had turned the pump down (full power screw) about a month ago to get my egts down, checked the locknut, still tight
adjusted the idle screw, until it idled at 750, drove it a little bit to test, idle held
Drove it yesterday (50km one way) when I started the truck to go home the idle flared up, as if starting an old carbureted V8, and came back down
except the idle was high again, this time about 900rpm
This increase of idle or full power is what worries me most. This pump shouldn't just change all by it'self
It doesn't seem to matter whether I start it hot or cold now it does the same flare up on every start up, and the idle seems to be getting closer to 950rpm.
I'm worried that something is worn out and hanging up inside my injection pump, and don't want to leave it until it fails possible taking out the pump, and leaving me stranded
especially as this truck is my sledding rig, having a failure on the side of the road in town is bad enough, but a failure 50 km (often more) back in the bush after a hard day of sledding, cold and in the dark.

Cummins experts any help and suggestions would be greatly appreciated!!!

tDIC

Ttt

tDIC

Update:
Drove the truck today, rolling lots of coal, much more than usual. Played around a little bit to see if anymore clues would show themselves. While doing that it seemed to have cleared itself. Idle dropped back down, and no more flare up at start up. Thinking there must have been a restriction in the return. I know there wasn't in the supply, no pressure drop across the filter, and seems like a supply restriction wouldn't self--heal.

That being said I'd still like to hear from you guys on this issue. Not convinced that it won't return or get worse.

Sasker

tDIC

How would an air restriction be intermittent, or self healing?

Sasker

tDIC

I see your point, air filter was one of the first things I checked though.

As far as the fuel return restriction goes, I thought maybe I had some rubber off the stopper on the fuel shut off solenoid, as I know that the pump has been turned up, and I'm not sure where it is in relation to stock. But I took the solenoid out tonight and it's mint. So I'm back to thinking something is up with the pump.

This afternoon when I drove it, it still had the start up flare, and pushed lots of black smoke (preboost, and past where it normally clears). Part way through the drive the black smoke amounts and when it smokes went back to normal. When I shut it off, I restarted to see, and sure enough no flare and idling below 750 (I had backed the full power screw out ½ turn to see what it would do on Sunday).

Turned the screw ½ turn back in and all has been well since

Alwaysworking

i would check the fuel pin and be sure its not sticking.that could cause some issues

tDIC

Took top of pump off yesterday. Fuel pin moves freely, as did the horizontal pin, AFC diaphragm good. The only thing that might explain my issues is there is rust scale covering the top section of the full power lever where it is above the fuel level. Maybe adjusting it's screw caused some rust to flake off partially obstructing an injector/s. I just don't have enough experience with these old Cummins to say. Aside from the flare up the truck starts good in cold weather. No white smoke, or chugging, idles smooth.